Han R
Laboratory of Immunology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
Immunol Invest. 1997 Jun;26(4):421-37. doi: 10.3109/08820139709022699.
The assembly of major histocompatibility complex (MHC) class II alpha and beta chains occurs in the endoplasmic reticulum (ER) with the involvement of MHC class II-associated invariant chain (Ii). The present study investigated the impact of Ii on the assembly of both I-A haplotype-matched and -mismatched alpha and beta chains using an in vitro translation system. The alpha and beta chains of I-Ab, I-Ad and I-Ak were cotranslated in vitro in different combinations with or without cotranslation of a truncated murine Ii (mIi 1-131). The translated products were sequentially immunoprecipitated, first with conformation-dependent monoclonal antibodies, then with conformation-independent antibodies. The results show: (1), Ii did not associate with free A alpha and free A beta chains; (2), mIi 1-131 significantly augmented the amount of properly assembled A alpha b A beta b, A alpha b A beta d, A alpha b A beta k and A alpha k A beta b dimers, but had little affect on the assembly of A alpha d A beta d, A alpha k A beta k, A alpha d A beta b, A alpha k A beta d and A alpha d A beta k; (3), All A alpha A beta dimers whose assembly could be significantly facilitated by mIi 1-131 could be coimmunoprecipitated along with substantial amounts of mIi 1-131. This finding is consistent with prior observations that the impact of Ii on class II molecule assembly is allele specific. Furthermore, these results suggest that the efficient assembly of alpha and beta chains is primarily determined by the affinity between alpha and beta chains and the the high affinity of mIi for A alpha A beta dimers is required for mIi 1-131 to assist proper A alpha A beta assembly, most probably through a mechanism in which Ii stabilizes properly assembled A alpha A beta dimers or promotes folding of associated alpha and beta chains to help achieve a stable dimer state.
主要组织相容性复合体（MHC）II类α链和β链在内质网（ER）中组装，MHC II类相关恒定链（Ii）参与其中。本研究使用体外翻译系统研究了Ii对I-A单倍型匹配和不匹配的α链和β链组装的影响。I-Ab、I-Ad和I-Ak的α链和β链在体外与截短的小鼠Ii（mIi 1-131）共翻译或不共翻译，以不同组合进行共翻译。翻译产物先用构象依赖性单克隆抗体进行顺序免疫沉淀，然后用构象非依赖性抗体进行免疫沉淀。结果显示：（1），Ii不与游离的Aα链和游离的Aβ链结合；（2），mIi 1-131显著增加了正确组装的AαbAβb、AαbAβd、AαbAβk和AαkAβb二聚体的数量，但对AαdAβd、AαkAβk、AαdAβb、AαkAβd和AαdAβk的组装影响很小；（3），所有其组装可被mIi 1-131显著促进的AαAβ二聚体都可以与大量的mIi 1-131一起进行共免疫沉淀。这一发现与先前的观察结果一致，即Ii对II类分子组装的影响具有等位基因特异性。此外，这些结果表明，α链和β链的有效组装主要由α链和β链之间的亲和力决定，mIi 1-131协助AαAβ正确组装需要mIi对AαAβ二聚体具有高亲和力，最有可能是通过一种机制，即Ii稳定正确组装的AαAβ二聚体或促进相关α链和β链的折叠以帮助实现稳定的二聚体状态。
